Insulin Resistance in Nonalcoholic Fatty Liver Disease: A Case Control Study

We hypothesize that insulin resistance is characteristic of nonalcoholic fatty liver disease as compared to age, gender, non-diabetic BMI-matched control subjects, both healthy and those with non-cirrhotic, non-steatotic liver disease.

Purpose of the study: To date, no case control study evaluating insulin resistance (IR) in nonalcoholic fatty liver disease (NALFD) has been published. We hypothesize that IR is characteristic of NAFLD as compared to age, gender, non-diabetic BMI-matched control subjects, both healthy and those with non-cirrhotic, non-steatotic liver disease. The following aims test this central hypothesis: Specific Aim 1: Measure IR and insulin clearance using intravenous glucose tolerance testing and Bergman's Minimal Modeling in patients with NAFLD as compared to matched controls (healthy and those with non-steatotic hepatitis). This aim tests the postulate that IR is necessary for the development of hepatic steatosis as compared to healthy (non-steatotic livers). It will also test the postulate that IR is not present as a confounding factor (impaired hepatic clearance) in NAFLD as compared to those with non-steatotic forms of hepatitis. Specific Aim 2: Determine if IR is associated with altered parameters of lipid metabolism as compared to matched controls. This aim addresses whether IR (if present) is associated with abnormal lipid parameters in NAFLD or can be observed irrespective of the presence of hepatic steatosis. Specific Aim 3: Measure the differential effects of IR and lipid metabolism on peripheral mononuclear cell (PBMC) inflammatory response and the associated hepatocyte mitochondrial ultrastructure and measures of oxidative stress. Since increased oxidative stress and bioenergetic failure have been associated with hepatic steatosis, this aim will address whether IR and/or steatosis results in impaired inflammatory response and increased oxidative stress as compared to controls. Changes in innate immune response will be determined by measuring inflammatory indices thought to correlate with obesity, IR, and/or chronic hepatitis: 1) interleukins (IL-2, IL-4, IL-6, IL-10, IL-12, IL-18) 2) C-reactive protein, 3) TNF-a and TGF-B 4) IFN-A \& IFN-g, and 5) adiponectin. Changes in oxidative stress will be determined by measuring key indices of oxidative stress and damage. These include, a) reduced and oxidized glutathione (GSH and GSSG); oxidation/reduction status), b) malondialdehyde (MDA;lipid peroxidation), c) nitrotyrosine (NO damage), and d) 8OHdG and 8OHG (DNA damage). Background and significance: Obesity, diabetes, hypertriglyceridemia, hypertension, and coronary heart disease constitute a phenotype common to individuals with either the IR syndrome or NAFLD1-12. Furthermore, the hepatic steatosis, fibrosis, and cirrhosis characteristic of NAFLD are also frequent histologic findings in patients with IR 3-7. Together, these data beg the question whether NAFLD and IR are causally associated. Support for this notion derives from recent observations that IR may be a strong, independent predictor of NAFLD, even in the absence of glucose intolerance 13. Moreover, since NAFLD has been reported to occur in lean subjects (BMI greater than 25) with normoglycemia 14, 15, it is reasonable to postulate that NAFLD may be an early manifestation and a consequence of IR. Increased oxidative stress is an important pathogenic mechanism of obesity-associated metabolic syndrome 16. Fat accumulation correlated with systemic oxidative stress in humans and mice. However, increase oxidative stress as an instigator of the metabolic syndrome in patients with NAFLD as compared to controls has not yet been investigated. Furthermore, impaired cytokine medicated inflammatory response has been shown to correlate with body mass index across the broad range of obesity and may mediate hepatic steatosis and/or lead to mitochondrial dysfunction in hepatocytes 17, 18. Discerning whether NAFLD is attributable to increased oxidative stress and/or abnormalities in innate immune response would be imperative in identifying potentially useful therapeutic targets for obesity-associated liver disease.